


The Secret Omega

by GeekCharming270



Category: Assassination Classroom
Genre: Alpha Akabane Karma, Alpha/Beta/Omega Dynamics, Consensual Underage Sex, M/M, Mating Cycles/In Heat, Omega Shiota Nagisa
Language: English
Status: Completed
Published: 2020-12-24
Updated: 2020-12-24
Packaged: 2021-03-11 00:15:40
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,495
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28295910
Author URL: https://archiveofourown.org/users/GeekCharming270/pseuds/GeekCharming270
Summary: Nagisa's mother kept his secondary gender a secret, but what happens when the March deadline is only a month away and Nagisa is about to go into heat and has to take time off of school?
Relationships: Akabane Karma & Shiota Nagisa, Akabane Karma/Shiota Nagisa
Comments: 8
Kudos: 202
Collections: Mating Instincts





	The Secret Omega

**Author's Note:**

> Two stories in one day?! Who is she? Haha, it's the giving season and multiple fics are my gifts to the readers this year.

The thing about being a male omega is that they were seen as lesser than their female counterparts. Sure, they still had regular heats and could give birth like female omegas, but for some unknown reason, society had deemed them as lesser. They still had all the same rights as female omegas, but as far as most people cared male omegas were useless. So, when he presented at the age of 12 Nagisa’s mother took it upon herself to make sure that no one would know the truth of what he was.

She bought the best heat suppressants and scent neutralizers money could buy and even went as far as lying on official forms, claiming that Nagisa had actually presented as a beta. So, for all intents and purposes, Nagisa Shiota was a male beta, but that never stopped his mother from making comments about how she knew that he should have been born a girl because then his omega status wouldn’t have been a problem.

Despite all his mother’s attempts to hide his true secondary gender, she couldn’t stop the blunet’s bi-yearly heats from happening. Granted the heat suppressants made it easier on Nagisa to deal with the usually crippling pain and sexual urges, but it couldn’t fully stop his biology from taking over.

That was what led to Nagisa’s current predicament. They were only two months away from the March deadline Koro Sensei had set and the boy’s heat was going to start the next day. He was going to be forced to miss the next three days of class and assassination attempts all because of his stupid heat.

With a heavy heart, the teen made his way into the Staff Room where all of his teachers were working at their desks. He just hoped he could tell them as little information as possible and so he could get home and prepare for the next three days. Koro Sensei, Mr.Karasuma, and Professor Bitch all looked up at him questioningly.

It was Karasuma who addressed him first, “Nagisa, what can we do for you?”

The omega blushed, “You see, Sir, I won’t be in class for the next few days and I just wanted to inform you all of my absence.”

“Is everything alright?” Karasuma asked.

A deeper blush filled his cheeks, “Everything is fine. I just need to take a few personal days.”

“Personal days?” The alpha replied unimpressed. “We can’t afford for you kids to be taking personal days right now.”

“I’m sorry, Sir, but there’s just no way for me to be in class the next three days.”

Karasuma looked like he wanted to yell, but Koro Sensei stepped in before he could, “It’s because you’re going into heat isn’t it, Nagisa?”

The omega should have been surprised that someone had guessed the reason for his absence, but Koro Sensei wasn’t exactly human, so really if anyone was going to find out the truth it was going to be him. Karasuma and Professor Bitch looked between the pair in shock as the teenager hung his head, nodding in confirmation.

“Well there’s really nothing we can do then,” Koro Sensei spoke again as he placed a comforting tentacle on the boy’s shoulder. “You go home and take care of yourself and when you get back I’ll help you catch up on what you missed. And don’t worry your secret’s safe with us.”

Finally, Nagisa managed to look the octopus in the eye with a shy smile, “Thank you, Koro Sensei.”

“You’re welcome, Nagisa. Now, why don’t you head on home.”

Nagisa bowed to his teachers and left the staff room with a smile on his face. That conversation had gone better than he had expected; now he just needed to get through the next three days and he could go back to pretending to be a beta and no one any wiser to his secret.

At least that’s what he thought. Just as he was about to grab his things from the classroom a familiar voice laced with anger called out to him.

“Nagisa.”

The omega turned to see the familiar form of Karma leaning against the wall directly next to the Staff Room, glaring at him. Even though he had known the redheaded alpha for three years now he was still intimidated. Every instinct told Nagisa to submit, but he held his ground; unrequited crush be damned.

“Hey, Karma. What’s up?” He replied cooly.

“Nothing much. Just wondering when you were gonna tell me that you were an omega,” Karma shot back nonchalantly.

If it weren’t for all of his training Nagisa would have frozen in place, but he quickly scanned their surrounding to make sure that no one else could hear them. Instead of letting himself be intimidated the blunet leveled his gaze at the alpha, “If we’re going to have this discussion then I’d rather be somewhere where there aren’t 26 assassins in training could overhear us. Just let me grab my things and then we can talk at my place.”

Surprisingly, Karma didn’t object, but rather followed Nagisa’s lead, grabbing his stuff and following the other boy out of the building. The silence was their only companion until they reached Nagisa’s apartment and the door was closed behind them.

“Do you want anything to drink?” Nagisa asked.

“No, thank you,” Karma replied, taking a seat on the couch.

The smaller boy could feel his heat starting to prickle beneath his skin and having a delightful smelling alpha nearby was making it hard to not present himself or bare his neck for the redhead. He needed to get this conversation over with as quickly as possible and get Karma out of the house so he could settle into his nest for the next three days.

As if sensing the change in his companion, Karma gently took one of the Nagisa’s hands in his own, squeezing lightly, “Nagisa, I’m not mad at you. I just want to know why you never told me that you were an omega.”

The floodgates seemed to burst with that simple statement because suddenly he was crying as he explained the truth of his secondary gender to his best friend; how his mother had always wanted a girl, forced him to grow out his hair, how she had decided to hide his secondary gender, the verbal and physical abuse, everything. Through it, all the alpha just sat there and listened, a look of reserved anger on his face the longer the tale went on, and when the story was over he pulled the smaller boy into a bone-crushing hug.

“I’m so sorry. I’m sorry I never saw how much you were hurting. I’m sorry that you didn’t think you could confide in me. You’re _mine._ I swear to you I’m never going to let her lay a hand on you ever again.”

Nagisa pulled away from the hug and stared into Karma’s eyes in confusion. How was he going to stop his mom from hurting him anymore and had he really heard Karma just claim him? They were just teenagers.

Karma must have seen the confusion because a trademark grin spread across his face as he pulled out his phone and made a call, “Father, I need you to take immediate custody of my classmate Nagisa Shiota.” Nagisa’s eyes widened as the conversation continued. “As soon as that’s done I need you to get ahold of his records and see that they are changed to state that his proper designation is omega. I’ll be bringing him home with me soon. We’re going to be in need of the heat room so if you could have the servants prepare it for us. Thank you. Goodbye, Father.”

“Did you just do what I think you did?” Nagisa squawked at the young alpha.

Another smirk, “Yup. Now let’s go grab your things and head home. I’m not letting you stay with that woman for one more night.”

Karma stood and led the other boy towards his room where they grabbed his few possessions and clothes that he actually cared for, packing them into a suitcase. The blunet was in a blur as Karma took his hand, leading him out of the apartment into the night air where a car was already waiting for them; the whole time his heat was boiling just beneath the surface of his skin. The driver got out and took Nagisa’s suitcase, placing it into the trunk while the two teenagers got into the backseat, Karma pulling Nagisa into his side, the calming scent of a burning fire washing over him. Instinctively the omega nuzzled into the scent as the other boy’s arms wrapped around him in a tender embrace.

After what seemed like an eternity the car stopped in front of a mansion, the door opening for them as Karma gently ushered Nagisa out of the car and up into the house. Waiting inside the doors was a tall man that was unmistakably Karma’s father with his piercing golden eyes and alphan demeanor, and next to him was a petite omegan woman with long red hair the same shade as his friend’s.

Immediately, the woman came forward and pulled Nagisa into a gentle hug, letting off calming pheromones that put the blunet at ease, something he had never felt around his own mother, “Welcome home, Nagisa.”

Another round of tears poured from the young omega’s eyes as he clutched onto the woman for dear life. They stayed like that for several minutes until Nagisa finally pulled back to look at Karma and his father who were smiling at the two omegas. Feeling slightly embarrassed he pulled away and bowed to the Akabanes, “It’s a pleasure to meet you. My name is Nagisa Shiota.”

It was Karma’s father who spoke next, “That’s enough with the formalities, Nagisa. My name is Ryo and this is my wife Sakura.” He gestured to the woman who Nagisa had been hugging. “As you might have guessed we’re Karma’s parents and your new guardians. From now on you’ll be staying here with us.”

“Are you sure? I don’t want to be a burden,” he replied sheepishly.

“That’s nonsense,” Sakura called. “Karma has never asked us for anything like this before. Whatever it was that happened with your old family must have been terrible, but that’s in the past now, you don’t have to worry about a thing.”

Nagisa wanted to cry again but maintained his composure, “Thank you. Words can’t describe how grateful I am.”

Karma smiled before leaving his father’s side and wrapping his arms around the smaller boy’s waist, “Is the heat room ready?”

As if summoned by his words Nagisa felt the itch of building heat beneath his skin, but it wasn’t nearly as bad thanks to the possessive grip and scent Karma was blanketing him with.

Ryo nodded, “There’s plenty of nesting material, food, and water for the both of you for the next few days.”

The smaller boy blushed at the implication in the older man’s words but said nothing as Karma released him, instead opting to take the handle of his suitcase in one hand and one of Nagisa’s hands in the other before leading him further into the house.

First, they stopped at a room Karma claimed as his own to drop off the suitcase before he was pulled further down the hall, stopping in front of a door that was made of the same golden wood as the rest of the house, but upon opening it Nagisa could see that the room was completely scentless, and was set up like a tiny apartment with a small kitchenette, bathroom, and an enormous bed dominating most of the space. Off to the side were piles of luxurious blankets and pillows that were also no doubt scentless and ready for use.

As the door shut behind them Nagisa turned to look at Karma as he spoke, “Why don’t you go take a shower and I’ll heat up some food for us. Then you can start building your nest before your heat takes full effect. And I’ll scent some of the blankets and pillows.”

Nagisa nodded and made his way into the spacious bathroom, stripping out of his uniform before stepping into the large waterfall shower, turning the water as cold as he could stand to try and lessen the heat building up in his body.

As the water cascaded down his body he couldn’t help but think about what was about to occur between himself and Karma. There was always something about the redhead that had drawn Nagisa in. Sure, he had some psychopathic tendencies, but beneath all that was a smart and caring guy who was willing to do anything to help his friends; the proof being himself.

Still, the thought of sharing his heat with the alpha he had been secretly in love with since they were first-years had slick leaking down his thighs and his cocklet weeping for attention. The urge to reach down and touch himself was intense, but Nagisa knew that as soon as he started he wouldn’t be able to stop, and he wanted to build a proper nest for them first. Using the soaps provided he managed to scrub off the layers of scent blocker and grime that had built up over the day until the scents of caramel and vanilla came through.

When he was done the blunet stepped out and toweled off with the fluffiest towel he had ever felt before donning a robe, making his way out to the main room where he was assaulted with the smell of an aroused alpha mixed with Italian spices. Karma was standing in the small kitchenette with two plates of spaghetti on the counter, his clothes discarded in exchange for a robe similar to the one Nagisa was wearing. When their eyes met there was only a slight ring of gold left in Karma’s lust-blown eyes and the scent of fire seemed to fill the entire room.

“K-karma is e-everything alright?”

The redhead seemed to struggle to find his words at first but finally managed proper speech, “Everything’s fine. I’ve just never been able to smell you before. It’s making my mouth water. Not to mention that your heat is making it even more potent than it would usually be. I’m having a bit of a hard time controlling myself right now.”

Nagisa closed the distance between them and released his own calming pheromones that seemed to take the edge off for the alpha. Silently, they ate the small meal Karma had prepared and then the redhead watched as Nagisa began weaving together a nest for them, taking his time to make sure it was perfect for his mate because at this point that’s what Karma was about to be, his mate. He was nearly done when guttural growls sounded from where the redhead was standing off to the side of the bed.

“It’s okay alpha. I’m almost done just hold on a little bit longer,” the omega purred.

That seemed to settle the young alpha for the time being. True to his word Nagisa only took a few more minutes to finish the nest to his satisfaction. Making his way out of the nest the blunet stood in front of Karma and without hesitation bared his neck to the alpha. A delighted growl left the other boy’s throat as he leaned down to nuzzle Nagisa’s exposed scent gland, combining their scents to make that of burnt sugar.

“Karma, _please_ ,” the omega begged, his hands going to the tie of his robe, discarding the garment.

Not wasting any time Karma untied the sash holding Nagisa’s robe closed, revealing the omega’s naked body. For several moments Nagisa waited anxiously as the alpha took in his appearance, “God, Nagisa, you’re gorgeous. I can’t believe I get to call you mine.”

Hesitant hands made their way to the tie holding together Karma’s own robe, silently asking for permission. With a nod the blunet undid the tie, pushing the fabric from the taller boy’s body reveling in the sight before him. Pale skin covering well-defined muscles and an enormous cock jutting straight up, pre-cum beading at the tip. It made Nagisa’s mouth water.

Not wanting to waste any more time the omega crawled into the nest he had constructed, beckoning Karma to follow him. The redhead did so enthusiastically, practically pouncing on the smaller boy.

“ _Mine!_ ” Karma growled, diving in and attacking Nagisa’s lips with his own.

There was nothing gentle about the kiss. It was filled with pure lust and arousal. Nagisa whined, his legs spreading subconsciously so his alpha would have better access to his weeping hole, “Please, _Alpha_!”

Karma pulled away from the kiss, letting his hands explore the body beneath him, drawing out little whines as he went, “And what is it that my little omega wants from me?”

“Need you…need your knot. Karma _please_!”

Then Nagisa felt a blunt pressure at his entrance. Looking down he saw Karma’s erection slowly slipping between his lips, the building friction flooding Nagisa’s body with even more need. Instinctively, the omega rolled his hips down so that even more of his lover’s cock was inside of him. All the smaller boy could do was moan until finally his alpha was fully seated.

Harsh panting filled the room as they stayed still for several moments until it all became too much for Nagisa. With more strength than he was aware of the omega rolled them over so that he was hovering over his lover, shoving the alpha’s cock even deeper. They both moaned, but a growl followed Karma’s at the display of dominance.

“ _Alpha_ ,” Nagisa practically yelled. “So good. Please alpha. Fuck me.”

Hands latched onto Nagisa’s hips with brushing force before Karma started to piston his hips up and down, forcing his cock in and out of the omega’s slick channel. There were no words to describe the pure bliss Nagisa felt as Karma fucked into him. Before when he had gone through his heats the only relief he had was his own hands. Now, with the real thing he couldn’t imagine going without his alpha’s cock ever again.

“Fuck! Nagisa!” Karma moaned. “So goddamned tight. So wet. Fuck, you’re perfect. Want you to come on my cock. Wanna fill you with my pups.”

Nagisa whined at the thought of carrying Karma’s pups. He had always wanted to be a mother, but because of his own mother, he doubted that it would ever come to fruition. Now that he was no longer under her thumb his dream could become a reality, and if he was with Karma then it was going to be truly amazing.

“Breed me, Alpha! Fill me with your pups! Want your knot!”

Karma continued to pound into the omega relentlessly. Nagisa was in heaven; his omega had never been satisfied so thoroughly before and he doubted above but Karma would be able to satisfy him ever again.

The sound of skin slapping skin filled the air as one thought made its way to the forefront of the omega’s mind. _Bite._ He needed his alpha’s bond mark on his neck, needed them tied together, needed the proof that he belonged to Karma.

As if sensing his thoughts the redhead leaned forward so that his mouth was level with Nagisa’s mating gland. Soft lips pressed against the sensitive flesh, causing the omega to cry out with need, _“Please Alpha!”_

With a deep growl Karma sunk his teeth into Nagisa’s mating gland. Fire licked through the blunet’s veins as the strongest orgasm he’d ever experienced washed over him.

His mind was in a pleasure-filled haze for he didn’t know how long until Karma’s soothing voice brought him back to reality, “Nagisa, are you okay?”

Nagisa smiled as his vision finally centered on the redhead smiling down at him, “Everything feels amazing.”

Karma laughed as he gently rolled them over so Nagisa was laying on top of him, their sexes still locked together because of the alpha’s knot. The omega purred as he nuzzled his face into his alpha’s neck. The combined scent of pleased alpha and omega filled the air of the heat room. They stayed like that until Karma’s knot went down and he gently pulled himself out. Nagisa whimpered at the loss, but Karma just laughed, “It’s ok. I’m sure we’ll be tied together plenty the next couple of days. But before we get going again I want you to mark me.”

The omega released even more pleased pheromones as he placed his mouth over Karma’s mating gland, opening his jaw wide before clamping his jaw down tightly. As the bond solidified itself burnt sugar filled the air and mentally they both sighed in relief at now being tied together.

“Thank you, Karma. For everything.”

“You don’t need to thank me. I only did the right thing and now you’re mine and I’m yours forever.”


End file.
